Reassessing the interpretation of current/voltage and steady–state photocarrier grating measurements in CH3NH3PbI3 perovskite films across device-operation temperatures

The temperature dependence of optoelectronic parameters in halide perovskites is challenging to access due to the interplay between ionic migration, electronic transport, and structural phase transitions. This study combines current/voltage J(V) characteristics and steady-state photocarrier grating (SSPG) measurements, integrating classical and perovskite-specific physics. The forward J(V) curves reveal a transition from a sub–Ohmic regime to higher-order regimes, governed by ion dynamics. Assuming that grain boundaries hinder ion diffusion, the time and temperature required for this transition provide critical material parameters. In solution-prepared MAPI films, we determine an activation energy of 0.43 eV for the apparent dielectric constant and a room-temperature ion diffusion coefficient of 1.4 × 10⁻¹¹ cm²/s with an activation energy of 0.48 eV, consistent with published values obtained by more sophisticated methods. Under illumination, J(V) curves show increased photoconductivity with temperature, with activation energies between 0.12 and 0.25 eV, explained by recombination dominated by shallow defects. SSPG measurements indicate ambipolar diffusion lengths of 100–200 nm at room temperature, increasing tenfold at 65 °C, i.e. in the cubic phase. This increase is attributed to a rise in dielectric relaxation time above the tetragonal-to-cubic phase transition at 40 °C, rather than enhanced carrier lifetimes, providing new insights into perovskite characterization.